Specific Aims: We plan to study the cell biology and biosynthesis of testicular sulfogalactosylalkylacylglycerol (SGG), the major glycolipid of mammalian testis. SGG appears to be made only in germinal cells and at a specific stage of differentiation when spermatocytes are moving from the basal to the adluminal compartment of the seminiferous tubule. We hope to determine the function of SGG by learning more about where it is made and its subcellular fate during differentiation. The following projects are planned: a) Cellular site of SGG sulfation. We have good evidence that SGG is sulfated in pre-pachytene spermatocytes. We hope to establish this more firmly by isolating germ cells enriched in SGG-sulfotransferase and by demonstrating a population of such cells in adult testis by autoradiographic methods following feeding of S-35 sulfate to rats. b) Intracellular location and site of synthesis of SGG. We know that SGG is sulfated in the Golgi apparatus and then moves to the plasma membrane. However, the mode of SGG insertion into plasma membrane during differentiation is not understood and will be studied by autoradiography at the electron microscope level. c) Biosynthesis of SGG. We have shown a rapid rise and fall of SGG-sulfotransferase during germ cell differentiation. We now also know that this control is due to the appearance of a sulfotransferase activator in pre-pachytene spermatocytes and an inhibitor in pachytene spermatocytes and round spermatids. We wish to purify both of these transferase modulators, to study their properties and to determine how they interact with SGG-sulfotransferase. The activator-inhibitor cycle may prove to be a model for the control of other enzyme activities during differentiation. d) The structures of protein-bound oligosaccharides on the surfaces of sperm and other geminal cells. Long-term Objectives: We hope to understand the role of SGG specifically, and of carbohydrates in general, during the differentiation of germ cells. It is possible that SGG serves to provide a signal which "opens" the "blood-testis" barrier (anatomically formed by Sertoli cells) to permit germinal cells to move from the basal to the adluminal compartment.